Dental gold alloy

ABSTRACT

THE INVENTION PROVIDES A LOW MELTING POINT PRECIOUS METAL OR DENTAL GOLD ALLOY CONSISTING OF GOLD, NICKEL AND GALLIUM OR GOLD, NICKEL, GALLIUM AND PALLADIUM. THE YELLOW GOLD ALLOY WHICH CONSISTS ONLY OF GOLD, GALLIUM AND NICKEL HAS A MELTING POINT OF ABOUT 1400*F. AND CAN BE CAST DIRECTLY TO PREFABRICATED PORCELAIN TEETH. ALSO, IT HAS A HIGH BRINELL HARDNESS AND HIGH TENSILE STRENGTH. THE WHITE OR PLATINUM COLORED DENTAL GOLD ALLOY, WHICH CONSISTS OF GOLD, GALLIUM, NICKEL AND PALLADIUM, HAS A MELTING POINT OF APPROXIMATELY 1500*F., HIGH BRINELL HARDNESS, AND HIGH TENSILE STRENGTH. BOTH ALLOYS ARE TARNISH RESISTANT.

United States Patent 3,574,610 DENTAL GOLD ALLOY Emil M. Prosen, Bala-Cynwyd, Pa., assignor to Nobilium Products, Inc., Philadelphia, Pa. N0 Drawing. Filed Nov. 1, 1968, Ser. No. 772,794 Int. Cl. C22c 5/00 US. Cl. 75-165 6 Claims ABSTRACT OF THE DISCLOSURE The invention provides a low melting point precious metal or dental gold alloy consisting of gold, nickel and gallium or gold, nickel, gallium and palladium. The yellow gold alloy which consists only of gold, gallium and nickel has a melting point of about 1400 F. and can be cast directly to prefabricated porcelain teeth. Also, it has a high Brinell hardness and high tensile strength. The white or platinum colored dental gold alloy, which consists of gold, gallium, nickel and palladium, has a melting point of approximately 1500 F., high Brinell hardness, and high tensile strength. Both alloys are tarnish resistant.

The present invention relates to precious metal alloys and especially to dental gold alloys.

More particularly, the present invention provides a dental gold alloy of relatively low melting point and relatively high Brinell hardness which can be cast directly to prefabricated porcelain teeth and which also can be used in making partial dentures, bridgework, crowns, inlays, veneers, orthodontic appliances, and gold Wire supplements,

Heretofore it has not been possible to cast a dental gold alloy directly to a prefabricated porcelain tooth for the reason, among others, that the melting temperatures of dental gold alloys and hence the casting temperatures of such alloys were so high that the porcelain would check or crack when subjected to the heat and other conditions of casting. Also, such dental gold alloys on cooling had a high rate of shrinkage as compared with the limited expansion and contraction of porcelain. Hence, the shrinkage problem presented another difficulty in trying to cast dental gold alloys directly to prefabricated porcelain teeth. In addition, dental gold alloys have usually included copper as a hardening element. Copper, however, is a non-precious metal which is attacked by food and other mouth acids and is prone to tarnish.

Generally speaking dental gold alloys in use today have a preferred carat value of 17 to 18, and usually include in addition to gold, copper and silver, and he quently some small percentages of platinum, palladium or iridium. Such dental golds usually melt around 1700 F. to 1800 F. and higher.

It is an object of the present invention to provide a dental gold alloy which can be cast directly to prefabricated porcelain teeth, which will have a melting point of about 1400 F., a Brinell hardness higher than that now attainable with dental gold alloys currently in use, and which has considerably less shrinkage than conventional dental gold alloys.

It also is an object of the invention to provide such a dental gold alloy which is free of copper and other tarnishable elements.

A further object of the invention is to provide such an alloy which has the natural yellow color of gold and which also can be modified to have a white or platinum color without seriously modifying the physical characteristics of the alloy.

The foregoing objects are accomplished with the present invention which provides a dental gold alloy having a yellow gold color which consists of gold, nickel and 3,574,610 Patented Apr. 13, 1971 gallium; and a dental gold alloy having a white or platinum color which consists of gold, nickel, gallium and palladium,

The preferred formula for the yellow gold alloy is:

Percent by weigh Gallium 4.6 Nickel 18.6 Gold 76.8

ing point of about 1400* F. and a Brinellhardness when rolled of 280 or slightly higher. It also has a high tensile strength, much higher than characterizes dental gold alloys currently in use.

It is well known that nickel has a melting point of 2600 F. and that gold has a melting point of 1945" F. The addition of the gallium apparently has a direct influence on the nickel and reduces its melting point to an unexpectedly low level. Furthermore, it appears that the gallium acts substantially to harden the nickel in almost the same Way as carbon acts on steel. The nickel imparts to the alloy toughness. Copper or silver are currently used in dental gold alloys to impart toughness. However, I have found that the nickel imparts more toughness while the gallium adds the hardness.

Also, the gallium brings down the melting point to a very desirable level, which in the preferred form of the invention is about 1400 F,

Another unique aspect of the present invention is from the standpoint of its color. Thus, I have found that even in the preferred formula which contains as much as 18.6% nickel, the yellow gold color is preserved. Thus, I have come to the conclusion that gallium seems to interfere with a change in color from yellow to white. In fact, as pointed out later, I have found it necessary to add from 6% to 8% palladium to change the color of yellow to white.

Additionally, because nickel does not tarnish and no copper is contained in the alloy of the present invention, I have found that alloys embodying my invention do not tarnish in the mouth of the user.

With the preferred formula for the yellow gold alloy of the present invention, which has a low melting point of about 1400 F. it has been found that this alloy can be directly cast to prefabricated porcelain teeth. The porcelain which is generally used by the dental profession is usually fused at a temperature of about 2400 F. Dental gold alloys which are currently available usually melt at around 1700 F. to 1800 F. or higher. The refractory material used in casting dental gold alloys can only be heated to 1350 F. Hence, it has not been possible heretofore to cast such dental golds melting around 1900 F. directly to prefabricated porcelain teeth in refractory molds which are only heated to 1350 F. The alloy does not cool-off sufficiently during casting and hence shocks the porcelain and causes fractures. With the alloy of the present invention which has a low melting point of about 1400 F. it has been found that the small differential in temperature between the alloy and the refractory mold can be dissipated very quickly and that the porcelain is not fractured by shocks during casting.

Also, dental gold alloys currently available shrink considerably on cooling and this shrinkage presents a problem when trying to cast such alloys directly to prefabricated porcelain teeth. It has been found that the alloy of the present invention using gallium has the unique characteristic that on heating it does not expand anywhere near as much as conventional dental gold alloys and that on cooling it exhibits considerably less shrinkage than conventional gold alloys. It is believed that this characteristic is due to the phenomenon that the gallium expansion and contraction characteristics on heating and cooling are opposite to those of the other elements in the alloy and hence serve to offset or partially counterbalance the same. In all events, the fact that the alloy of the present invention exhibits considerably less shrinkage than other dental gold alloys contributes to its use in direct casting to prefabricated porcelain teeth which have limited expansion and contraction under heating and cooling casting conditions.

A further advantage of the preferred yellow gold formula of the present invention is that with its high Brinell hardness and its high tensile strength it lends itself to considerably more uses in dental, professional and laboratory work. It can be used in preparing partial dentures, bridgework, crowns, inlays, veneers, orthodontic appliances and gold 'wire supplements, all of which will have improved tensile strength, hardness, and resistance to tarnish.

Another reason for favoring the preferred formula is that it is an economical formula and reduces the price at which the gold alloy can be sold. With 18.6% nickel and 76.8% gold it is approximately an 18 carat alloy. In dental work a 17 to 18 carat alloy is preferred as a minimum, although there are some economical alloys which are of lesser carat. Other dental alloys currently in use of no higher than 17 to 18 carat are much more expensive because they include platinum, palladium and iridium, all of which add to the cost in comparison with the use of nickel and gallium, "while providing less desirable physical characteristics for the dental gold alloy.

While I have set forth the preferred formula for the yellow gold alloy consisting only of gold, nickel and gallium, in the stated percentages by weight, and that such alloy has a melting point of about 1400 F., I have found that this low melting point can be retained with a 21 carat alloy having about 87% gold, with the nickel and gallium in correspondingly reduced percentages but in the approximate proportion of 4 nickel to 1 gallium. The following tabulation shows three yellow gold alloys prepared according to the present invention which are resectively 18 carat, 20 carat and 21 carat, each of which has a melting point of about 1400 F.:

18 carat 20 carat 21 carat gold gold gold Gallium 4. 60 3. 50 2. 42 Nickel 18. 60 12. 50 9. 80 Gold 76. 80 84. 87. 78

Gallium From 5% to 1% Nickel From 20% to 5% Gold Balance According to the present invention I have also found that I can provide a white or platinum colored dental gold alloy by adding a small percentage of palladium and correspondingly reducing the percentages of gallium, nickel and gold.

The preferred formula for a platinum-like or white gold alloy is:

Percent by weight Gallium 1.5 Nickel 2 l Palladium 6 Gold 71 This is the equivalent of 18 carat gold and has a melting point of about 1500 F. While this alloy can also be cast directly to prefabricated porcelain teeth, I prefer to use the yellow gold formula for this purpose. This platinumlike or white gold alloy possesses all of the other advantages of the yellow gold alloy and is especially adapted for use in partial dentures, bridgework, crowns, inlays, veneers, orthodontic appliances, and gold wire supplements. It has the desired high Brinell hardness and tensile strength for such uses. As a general rule I have found that with the white dental gold alloy of the present invention the relationship of the nickel with the gallium should be in the ratio of 6.5% to 1% and that the percentage of palladium should closely approximate 6%, the balance of the alloy being gold.

From the foregoing specification it will be understood, and I have found, that contrary to what has been done in the art heretofore, gold can be alloyed with nickel and gallium in suitable proportions to produce a yellow gold alloy which has physical and chemical characteristics far superior to the like characteristics of dental gold alloys currently in use; and that by the addition of palladium to such yellow gold alloy I have produced a white gold alloy which also is far superior in physical and chemical characteristics to the dental gold alloys currently in use.

As before stated, in the preferred forms of the dental gold alloys of the present invention I do not use any copper as this is a tarnishable element. However, it is within the purview of the invention to use some copper and silver and thereby partially reduce the gold and nickel content of the alloy, if tarnishing is not considered to be objectionable.

While the present invention has been described in its preferred forms it will be understood that various changes may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

What I claim is:

1. A precious metal alloy having a melting point above 1350 F. and below 1700 F. of high Brinell hardness and high tensile strength and consisting of nickel from 20% to 5%, gallium from 5% to 1%, and the balance gold.

2. A dental gold alloy having a melting point above 1350 F. and below 1700 F., of high tensile strength and high Brinell hardness, and consisting of nickel and gallium in the proportions of 5% nickel to 1% gallium and the balance gold.

3. A dental gold casting alloy according to claim 2 having a melting point of approximately 1400 F. and consisting by weight of 4.6% gallium, 18.6% nickel, and 76.8% gold.

4. A precious metal alloy according to claim 1 to which has been added approximately 6% palladium with the other elements correspondingly reduced in proportion.

5. A dental gold alloy having a melting point of approximately 1500 F. and high Brinell hardness and tensile strength consisting by weight of approximately 6% palladium, nickel and gallium in the ratio of approximately 6.5% nickel to 1% gallium, and the balance gold.

6. A dental gold alloy according to claim 5 consisting by weight of 71% gold, 21.5% nickel, 1.5% gallium and 6% palladium.

References Cited UNITED STATES PATENTS 2,050,077 8/1936 Wise 75134 3,134,670 5/1964 Prosen 75171 3,134,671 5/1964 Prosen 75-l72 3,254,279 5/1966 Cohn et al. 75-165X 3,340,050 9/1967 Nielsen et al 75-165 3,413,723 12/1968 Wagner et a1. 75l65X L. DEWAYNE RUTLEDGE, Primary Examiner E. L. WEISE, Assistant Examiner US. Cl. X.R 75-134T 

